America's Cup catamarans built for speed

Updated 3:49 pm, Saturday, June 8, 2013

Artemis Racing's catamaran makes a test run on the bay last month. The hydrofoil extends from the boat into the water.

Artemis Racing's catamaran makes a test run on the bay last month. The hydrofoil extends from the boat into the water.

Photo: Sander Van Der Borch, Sander Van Der Borch / Artemis R

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America's Cup catamarans built for speed

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(05-10) 11:25 PDT SAN FRANCISCO -- They are billed as the world's fastest sailboats, and the specialized 72-foot catamarans for the America's Cup challenger series and regatta are like sailing on the edge.

"These boats can be extremely dangerous," said Michael Rogers, captain of Adventure Cat, a sailing catamaran charter company in San Francisco, and a 25-year veteran of sailing on the bay. "They are essentially Formula 1 cars on the water."

The boats are equipped with a rigid 131-foot wing sail that can propel them at top speeds but also can't be reduced in size to slow down.

Most competitors, including Artemis Racing, the Swedish team involved in Thursday's tragedy, have also equipped their boats with hydrofoils. Those are horizontal underwater wings attached to a vertical plank extending into the water, like a rudder or dagger board, that allow the boat's hulls to lift out of the water at speed.

Flying over water

The combination means the catamarans can essentially fly over the water up to 46 mph, but it also makes them less maneuverable.

The wrecked Artemis boat had small hydrofoils visible, but it's unclear if it was equipped with hydrofoils capable of lifting the hulls out of the water.

The speed advantage of hydrofoils became clear after Emirates Team New Zealand unveiled them on its America's Cup boat last fall. Oracle Team USA, which wrecked a 72-foot boat on the bay in October, then incorporated them.

In a February training session, Oracle's boat was notably quicker than Artemis', which had only small foils to help reduce drag but which were unable to lift the hulls clear of the water.

Afterward, Artemis said its boat would be modified to become "fully foiling," according to an account on the official America's Cup website in March.

A crewman on the boat that towed the crumpled Artemis catamaran to Treasure Island after Thursday's accident said the wrecked boat had hydrofoils. But it's not known what caused the boat to capsize.

Tricky handling

The design of the boats, particularly a wing sail that can't be reduced to slow the craft, make them particularly difficult to handle in the tricky, shifting winds of the bay, Rogers said.

"These guys are great sailors. I don't think it was a failure of seamanship here," Rogers said. "They're tying to sail these boats literally on the edge."

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